Fossils and Fossilization

Part I: Fossils and Fossilization

Fossils and Fossilization

  • Fossils:

    • Remains, traces, or imprints of once living organisms preserved in the Earth's crust since some past geologic or prehistoric time.

Fossils and Evolution

Fossilization Process

  • Fossilization is a random process, leading to many gaps in the documentation of evolutionary history.

Types of Fossils

  • Body Fossil:

    • Physical remains (exo/endo/basal skeletons)

  • Trace Fossil:

    • signs of organic activity, burrowing, motion (track/strails)

Factors Favouring Fossilization

  • Two key factors:

    1. Possession of hard parts

    1. Quick burial

Types of Preservation/Fossilization

I. Unaltered Remains

  • hard skeletons or soft parts that remain unchanged.

  • soft part = insect in amber

  • hard skeleton = cenozoic shell - bivalve

II. Altered Remains

1. Carbonization

  • volatile constituents (oxygen, hydrogen, nitrogen) are removed from the organic compound, leaving only carbon as a thin black film.

    • Commonly found in anaerobic environments (Burgess Shale)

2. Recrystallization

  • alteration of less stable inorganic compounds (e.g., aragonite) into more stable ones (e.g., calcite) without a chemical or compositional change.

3. Replacement

  • Original minerals of the skeleton dissolve and are replaced by other mineral substances (e.g., silica, pyrite).

    • forming a replica of the original structure.

    • Example: Silicified/petrified wood found in the stone forest in National Park, Arizona.

4. Permineralization

  • mineral/chemical deposit in holes/pores, most original still there

5. Imprints, Moulds, and Casts

  • Organic structures can leave impressions if pressed into soft, capable materials (e.g., clay).

Imprints

  • impression made by thin objects (fish, leaves)

Moulds

  • impression of skeletal remains on rocks (external or internal).

Casts

  • organism leaves a mould, filled with sediment/minerals - replica of original

Geological Uses of Fossils

A) Age Determination

  • Fossils are used to determine the relative ages

  • certain organisms only existed during certain time periods

B) Correlation

  • strata connects dif. areas, establishes timeline

C) Paleo-Environmental Analysis

  • some organisms can only live in certain areas, helps predict climate conditions

D) Record of Life & Evolution

  • Fossils provide a record of prehistoric life, particularly for forms lacking living representatives, such as dinosaurs.

  • evidence for organic evolution and the succession of fauna and flora.

Classification of Organisms

Historical Context

  • Linnaean taxonomy:

  • Kingdom

  • Phylum

  • Class

  • Order

  • Family

  • Genus

  • Species

  • Super- or Sub- occasionally used for some groups.

Evolution of Classification Systems

  • Current classification commonly divides organisms into five kingdoms:

    1. Monera (bacteria)

    2. Protista

    3. Fungi

    4. Plantae

    5. Animalia

  • Coexists with a system dividing life into two primary divisions: Prokaryote (bacteria) and Eukaryote (animals, plants, fungi, and protists).

  • Prokaryotes vs Eukaryotes: DNA loosely distributed vs. in nucleus

The Three Domain Paradigm of Woese

  • Archea, Bacteria (P) and Eukarya (E)

Extinctions

Five Notable Mass Extinctions in Earth History:

  1. Late Ordovician (~440 million years ago)

  2. Late Devonian (~370 million years ago)

  3. End Permian (~245 million years ago)

  4. End Triassic (~210 million years ago)

  5. End Cretaceous (~65 million years ago)